Don't mess with your pH. It causes more problems than it solves.
Fish that like low pH usually like soft water as well. Adding chemicals to the tank to reduce the pH just increases the mineral content of the water, the opposite of what soft water fish want.
Most pH reducing chemicals only have a temporary effect; the pH soon bounces back to what it was and this constantly changing pH is bad for the fish.
So long as you don't have a high carbonate hardness, things like lots of bogwood or even peat in the filter can help to lower pH, though in these cases it is better to a lot of small water changes so you aren't adding a lot of water with different pH in one go. [ not garden peat as that contains plant fertiliser]
Most fish can live quite happily in water that is the 'wrong' pH. Hardness is actually more important than pH. Few soft water fish can tolerate very hard water, and hard water fish will suffer in very soft water.
Do you know the hardness of your water? It should be somewhere on your water supplier's website.
It is possible to have soft water with high pH - mine is medium soft with a pH of 7.4. This means I can keep soft water fish that prefer a low pH rather than hard water fish that like a high pH.
